Clinging to existence

A Pacific pocket mouse peeks out from a small plastic pipe in its cage at the San Diego Zoo Institute for Conservation Research in Escondido, where it is part of a captive breeding program.   (Don Bartletti / Los Angeles Times)

The top priorities of the Marines at Camp Pendleton include ensuring the security of the United States and the survival of a nearly extinct mouse. Biologist Cheryl Brehme of the U.S. Geological Survey monitors the California pocket mouse population at Camp Pendleton last month.   (Christina House / For The Times)

The Marine Corps and U.S. Fish and Wildlife Service joined forces with the San Diego Zoo Institute for Conservation Research to establish a captive breeding program with 22 pocket mice. The mice, which feature a fur-lined pouch on each cheek and weigh no more than a silver quarter, are being held in quarantine at the institute’s veterinary center.   (Don Bartletti / Los Angeles Times)

Biologist Cheryl Brehme of the U.S. Geological Survey monitors the California pocket mouse population at Camp Pendleton. The mouse is one of 16 threatened or endangered species that share the base.   (Christina House / For The Times)

A biologist views the tiny footprints of the California pocket mouse, whose existence is on shaky ground, with only hundreds remaining in the wild.  (Christina House / For The Times)